The present invention relates to a flat, cooling device to be used in a pit furnace such as a blast furnace, or the like, having a fireproof lining or casing; and more particularly, the invention relates to a copper plate or a low-alloyed copper plate to be used for cooling such a furnace and having internal cooling channels.
Flat cooling devices or plates of the type to which the invention pertains are usually arranged between the shell of such a furnace, e.g., a blast furnace, and a brick lining thereof. The cooling ducts or channels are connected to a suitable circulation system for a coolant. The cooling plates themselves are covered on one side with a fireproof lining, the side being the one facing the interior of the furnace.
Plates for cooling, having the foregoing features, are known to be made of cast iron; and pipes are embedded therein. The heat transfer through these plates is quite poor for two reasons. For one, the thermal conductivity of cast iron is rather low; the other reason is an added resistance against heat flow across the pipe-plate interface; there may even be a gap, oxide layer, or both.
In some cases, the brickwork of the furnace casing is damaged, deteriorates with age, etc., so that the inside surface of the cooling device is, locally at least, directly exposed to the hot furnace chamber. Since the operating temperature of a blast furnace is well above the melting point of cast iron and since the poor heat transfer conditions through the plate (supra) do not lead to adequate cooling of the inside surface of the cast iron plate, the plate will wear out and deteriorate rather rapidly. Thus, the life of such a cooling device is quite limited.
Another known variety of cooling plates is made of cast copper, either being directly provided with internal cooling ducts, or tubes for the coolant are embedded in the cast. The texture of cast copper is not as homogenic and dense as the texture of forged or rolled copper. Thus, the heat transfer through cast copper is not as good as through a denser and more homogenic copper. Also, cast copper is not as strong. Moreover, separate, embedded cooling tubes inevitably carry an oxide layer which impedes the heat transfer into the tubes. On the other hand, integral ducts in cast copper plates have frequently rather rough walls and uneven surfaces. The surfaces may even carry embedded sand from the casting. All of these features reduce the heat transfer into the ducts.